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If you choose Resource Assessment as , the Function or Modelled Variable will will be evaluated before each Resource Assessment System is processed. This could obviously result in If there are multiple Resource Assessment systems, then there will be multiple evaluations.
Ordering/Flow Phase Time of Evaluation
Each function can be used in one or more model inputs. Each model input . As the ordering phase moves up the network, or as the flow phase moves down the network, the Function or Modelled Variable will be evaluated before each element it is used at. As an example, if you have used a function at 2 inflows, and have selected Order Phase as the time of evaluation, then the function will be evaluated twice in the order phase, once before each inflow where it is used. If the Function or Modelled Variable is used at an input which is not a network element, then it will be evaluated once before the phase begins.
Which Time of Evaluation(s) to choose
A lot of the power, and confusion, when setting up a function is based around when to choose to evaluate a function or modelled variable. One important note here is that there will most likely be multiple solutions which will work. To understand where each of the choices fits in within the larger scheme of the model phases please review .... ..
Suggestion: Each element in Source is evaluated at a different time-step, depending on its .... (what word can be used here?).
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Introduction to function ToE
A few words talking about the two types available - ie. functions & modelled variables.
Functions Time of Evaluation
Anu: The key to choosing the time of evaluation for a function is to consider its usage. For example, if a function is used in a Resource Assessment system, then it is ideally evaluated in the Resource Assessment phase. ((Next sentence: Leave as is))The way to decide which time of evaluation to choose, is to look at where the function is being used. As an example, if you are using the function in a Resource Assessment System, then ideally the function will be evaluated in the Resource Assessment phase. Likewise, if you are using the function to drive the demand on a time series demand model, then you would want to choose the ordering phase to evaluate the function. UNCLEAR: In In cases where you are using the function in at multiple placesinputs, you will have to decide whether its appropriate may want to evaluate the function in at multiple phasespoints.
Modelled Variable Time of Evaluation
Modelled variables are designed to read data from the model, to be used as part of an equation in a function. Which Time of Evaluation you choose will depend on when the data you need will be available. For example, if your modelled variable is pointing to the downstream flow of a node, then that data will only be available after the flow phase, so using the Post Flow Phase Time of Evaluation would most likely to be correct choice. End of Time Step would also work in this case.
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